1. Field of the Invention
The present invention relates to integrated circuits and, more specifically, to user-programmable integrated circuits. More particularly, the present invention relates to user-programmable mixed analog and digital integrated circuits.
2. The Prior Art
General purpose linear integrated circuits have limited themselves to specific functions such as operational amplifiers, phase locked loops, comparators, A/D converters, video amplifiers, transistor arrays, etc. These circuits form the building blocks of analog systems. Integrating these circuits into higher functions is difficult due to the need to employ external components (i.e., resistors, capacitors, inductors, etc.) to determine their exact function. Thus once integrated, these circuits become specialized, In order to be practicable for design, manufacture, and sale, such a specialized part must have a large usage base. One illustrative example of such a circuit is an audio amplifier which may be used in stereo systems or television sets. Without a large usage base, the design and manufacture of such a circuit is not economical.
During the manufacture of analog circuits a significant cost is the final trimming of each individual circuit. This is required because component values vary as well as stray capacitance due to component placement.
Another common problem in electronics is that various parts of a complex signal need to be kept in phase while utilizing different circuit paths. This is commonly done in color television sets where the luminance information is routed through a delay line while the chrominance information is processed.
Furthermore, many common analog systems such as television sets, VCR's and stereo systems are currently employing many digital functions. Hence the integration of these circuits onto a single integrated circuit die requires mixed analog and digital design and a process to manufacture them. The manufacturing process for such integrated circuits is complex and expensive as the transistors used in analog circuit design are typically radically different from those used in digital design.
One prior-art approach to this problem has been to design circuits which operate employing digital signal processing (DSP) techniques. These devices use a microprocessor core to simulate the mathematical equivalent of the analog system. One common application for such chips is digital filtering of the signals before conversion back to the analog world.
A fundamental limitation of these integrated DSP devices is that the device speed is limited by the Von Neuman architecture of the microprocessor where many processor functions are required for each time slice of the analog signal. This limitation has heretofore limited the speed of such devices to frequencies in the audio spectrum. This is of course due to the fact that the customization of the function is achieved by the coding of the instructions in the microprocessor.
Another approach to the mixed analog and digital integrated circuit is shown in U.S. Pat. No. 5,107,146 to El-Ayat. This patent discloses a user-programmable architecture including a mixture of analog and digital circuit modules. The digital logic modules are of the type used in prior field programmable gate array (FPGA) devices.
Work has been done in the past in trying to design processor arrays to speed up applications. These class of machines are called MIMD or SIMD (multiple instruction multiple data or single instruction multiple data). These concepts utilize a plurality of processor engines to perform logical operations, such as multiplication and division. Each processor engine is a Von Neuman machine and occupies significant die area on an integrated circuit.
It is an object of the present invention to provide a user-programmable digital signal processing integrated circuit which overcomes the limitations of the prior art.
It is another object of the present invention to provide a user-programmable digital signal processing integrated circuit which does not require individual trimming to maximize performance.
Yet another object of the present invention is to provide a user-programmable digital signal processing integrated circuit which allows the user to control phase shifting of signals being processed therein.
It is a further object of the present invention to provide a user-programmable digital signal processing integrated circuit which may be easily programmed by a user.